基于激光回馈效应的纳米计量系统

Nanometrology system based on laser feedback effect

提出了一种基于激光多重回馈效应的纳米计量系统,系统采用非准直平凹回馈外腔结构,使在回馈外腔中往返多次的回馈光束返回到激光谐振腔中,形成高阶回馈效应,得到了高密度、类正弦和位相正交的双频激光回馈条纹。条纹的密度为传统弱回馈的几×10倍,而且回馈条纹以激光波长为尺子,具有可溯源性,在没有任何电细分的条件下达到了nm级的光学分辨率。特别地,通过采用双折射双频激光器,获得了两偏振正交的激光回馈条纹,而且两正交偏振回馈条纹间还具有位相差,位相差的大小主要由双频激光器的频差、外腔长以及回馈阶次决定。利用两正交偏振回馈条纹间的位相关系,可用于识别物体的运动方向。与激光干涉仪的比对实验表明,系统的线性度优于5.2×10-5,光学分辨率为10.2nm,量程大于500μm。

Nanometrology is the measurement standard of nano-materials and nanometer devices, which is important for the development of nano-scieenee and nano-technology. A nanometrology system based on laser multiple-feedback effect is presented is this paper. This nanometrology system consists of two parts：a plane mirror and a concave mirror, which is also called parallel-concave feedback cavity. The high density cosine-like intensity fringes with phase-quadrature are obtained due to the laser multiple reflec- tions in the parallel-concave feedback cavity. The intensity of fringes is dozens of times of that of conven- tional weak feedback. The feedback fringes have nanometer level resolution without any electronic subdi- vision and can be traeeable to the light wavelength. Two polarization polarized feedback fringes are ob- tained by using a birefringence dual-frequency laser. Especially, there is a phase difference between the two polarization polarized fringes. The phase difference is mainly determined by the frequency difference of laser, the length of external cavity and the feedback order. Furthermore, the direction of displacement can be determined conveniently by using the phase relationship between two polarization polarized frin- ges. The experimental results compared with laser interferometer demonstrate that the linearity is better than 5.2 ×10^-5,optical resolution is 10. 2 nm,and the measuring range is more than 500μm.